U.S. Pat. No. 4,239,519 describes the preparation of inorganic, crystal-containing gels and papers, fibers, films, boards, and coatings produced from those gels. The process for preparing the gels comprised three basic elements:
(a) a fully or predominantly crystalline body is formed (a glass-ceramic is the preferred embodiment) which contains crystals consisting essentially of a lithium and/or sodium water-swelling mica selected from the group of fluorhectorite, hydroxyl hectorite, boron fluorphlogopite, hydroxyl boron phlogopite, and solid solutions between those and other structurally-compatible species selected from the grop of talc, fluortalc, polylithionite, fluorpolylithionite, phlogopite, and fluorphlogopite; PA1 (b) that body is contacted with a polar liquid, conveniently water, to cause swelling and disintegration of the body accompanied with the formation of a gel; and PA1 (c) the solid:liquid ratio of the gel is adjusted to a desired level depending upon the application therefor. PA1 Li.sub.2 O: 0-12 PA1 Na.sub.2 O: 0-10 PA1 Li.sub.2 O+Na.sub.2 O: 0.5-14 PA1 MgO: 10-38 PA1 B.sub.2 O.sub.3 : 0-30 PA1 Al.sub.2 O.sub.3 : 0-10 PA1 SiO.sub.2 : 35-70 PA1 F: 0-15 PA1 OH: 0-15 PA1 F+OH: 4-15 PA1 (1) a primary amine solubilized with acid; PA1 (2) a secondary amine solubilized with acid; PA1 (3) a tertiary amine solubilized with acid; PA1 (4) a quaternary ammonium acid salt; PA1 (5) a quaternary phosphonium acid salt; and PA1 (6) a ternary sulfonium acid salt.
Particularly useful base compositions are stated to consist essentially, expressed in terms of weight percent on the oxide basis, of
To confer good chemical durability to papers, films, fibers, boards, and coatings produced from the gels, those products are contacted with a source of large cations to cause flocculation of the gel and an ion exchange reaction to occur between the large cations and the Li.sup.+ and/or Na.sup.+ ions from the interlayer of the crystals. Normally, the ion exchanged products will be subsequently washed and dried. The patent discloses K.sup.+, Rb.sup.+, Cs.sup.+, NH.sub.4.sup.+, H.sub.3 O.sup.+, Ca.sup.+2, Sr.sup.+2, Ba.sup.+2, Pb.sup.+2, Cu.sup.+, Ag.sup.+, and certain organic polycations, specifically naming aniline hydrochloride and quaternary ammonium compounds, as illustrative of large cations operable in the ion exchange reaction. If desired, the ion exchange may be carried out with the gel, i.e., before a paper, film, fiber, board, coating, or other product is fashioned, or during the process for actually forming the product. In any event, no matter where the ion exchange is conducted in the stream of production, its occurrence is demanded to avoid spontaneous disintegration of the products in the presence of water.
Long term testing of articles formed in accordance with the description of that patent has demonstrated that the values of such physical properties as mechanical strength, flexibility, dielectric strength, loss tangent, and ionic conductivity are modified by the relative humidity of the ambient environment. In other words, the properties exhibited by the products do not manifest long term stability when exposed to humid atmospheres. Thus, there is normally an overall deterioration in the electrical and mechanical properties as the relative humidity of the surrounding environment is increased.
The use of finely-divided mica as an inexpensive filler in organic plastics has long been practiced. Hence, the mica not only reduces the cost of the products but also stiffens the plastic so that mold shrinkage is considerably reduced. However, the loading of mica into the plastic is commonly held below about 30% by weight since the mechanical strength of the product is adversely affected at higher loadings. Very recently (Rosalind, J., "Non-Fibrous Reinforcements", Modern Plastics, July, 1982, pages 46-48) it has been shown that, by utilizing certain forming conditions and practices, the flexural strength and Young's modulus of the plastic product can be increased as much as threefold through loadings of mica of 40-50% by weight. The absolute strength of the final article will still customarily be less than that imparted through glass fiber reinforcement but the mica provides other advantages. Thus, the mica flakes tend to assume parallel orientation during the flow of the plastic, thereby resulting in a "fish-scale" structure which resists point impacts, infiltration, and corrosion. Moreover, the mica flakes can be packed much more solidly than glass fibers which permits advantage to be taken of high volume content in this composites.
As is explained in U.S. Pat. No. 4,239,519, the crystals developed exhibit a morphology of a continuum of flakes, rectangular-like strips, and interwoven ribbons in parallel or sub-parallel zones or sheaths with said flakes being irregularly shaped with diameters between about 0.5-10 microns and cross sections of less than 100 .ANG., and said strips and ribbons being about 0.5-10 microns long, about 500-5000 .ANG. wide, and less than about 100 .ANG. thick. Such morphology results in the crystals demonstrating a very high aspect ratio, higher than naturally-occurring mica, and large surface area, both of those features serving to recommend the utility of the materials for reinforcing plastic bodies.